Panels which are made from steel sheets or similar materials are often obtained from a factory with prepunched holes which are designed for mounting parts, such as electric parts. These preliminary holes, which have diameters of about 20 mm, very often must be enlarged to diameters which are several times greater in size. Such an enlargement operation is usually fulfilled with the use of a portable hydraulic punching tool which comprises a cylindrical handle which forms an oil reservoir and is connected to a cylindrical portion of a larger diameter. This larger-diameter portion forms a hydraulic cylinder actuated by a manual hydraulic pump driven from a pivotally connected hand lever. The pump sucks a hydraulic fluid from the above-mentioned reservoir for supply under pressure to the above-mentioned cylinder. A ram of this hydraulic cylinder is connected to a punching rod. When hydraulic pressure is applied to the punching rod and the rod is moved, it compresses a coil spring which engages the ram and accumulates energy for the return stroke of the ram. The actual operation is performed by fitting a fixed die, which corresponds to the diameter of the enlarged hole, via a distant collar onto the punch rod which projects from the hydraulic cylinder. The punch rod is passed through the above-mentioned preformed hole of the sheet panel, and then a piercing punch, which cooperates with the fixed die, is screwed onto a threaded portion of the above-mentioned rod from the opposite side of the steel sheet. When the punch rod is moved, the portion of the steel sheet which is clamped between the piercing punch and the fixed die is sheared, and as a result, the preformed hole is enlarged to the required diameter.
A typical punching tool of the type described above has a 200 mm-long housing, a 120 mm-long punch rod portion projecting from the housing, and a 320 mm-long overall dimension. It is understood that the punching tool of such a size cannot be used in narrow spaces.
It has been proposed to provide a device consisting of a hydraulic cylinder and a punch rod connected to a ram of the above-mentioned cylinder with the punch separated from the unit connected to a portable manual hydraulic pump via a high pressure hose. The use of a separated punch unit, however, required an assistance of an auxiliary worker. Without the help of an auxiliary worker it would not be so easy to perform the punching operation.
The author of the present patent application has made an attempt to solve the above problem by providing a hole-piercing punch with a hydraulic cylinder having a projecting rod, the cylinder being arranged perpendicular to the axis of a manual hydraulic pump and supported pivotally and in a cantilever manner. This device is described in Japanese Utility Model Publication No. 62-72,727. The piercing punch of the above-mentioned type is shown on the left side of FIG. 6. In this drawing, reference numeral 1 designates a hollow cylindrical handle, 2 is a hand lever, 3 denotes a manual hydraulic pump, 4 is a hydraulic cylinder, 5 is a punch rod, 6 designates a distance collar, 7 is a fixed die, and 8 is a punch.
The punching tool of the above-described type has a shorter overall length and therefore, similar to a separated punch, could be used in narrow spaces. Punching could be easily performed without the help of an auxiliary worker. Freedom in selection of an angular position with respect to the manual pump of hydraulic cylinder 4 with punch rod 5 provides easier control of hand lever 2.
There may be cases, however, when configuration of a sheet-metal object to be treated may cause problems for the use of this tool. For example, when, as shown in FIG. 6, punch rod 5 is installed in a position perpendicular to a vertical portion of sheet-metal casing 9, there may be not enough room for positioning the tool in the vertical direction, and handle along with hand lever 2 must inevitably project from the casing in the downward direction. If there is no access from the bottom, it would be quite difficult to operate handle lever 2.
The present invention is aimed at the solution of the above problem by providing a piercing tool which has a handle and a hand lever that is switchable between perpendicular and parallel positions with respect to the punch rod projecting from the hydraulic cylinder.
This objective is achieved by a punching tool which comprises a hollow cylindrical handle with an oil reservoir within it, a manual hydraulic pump, and a hydraulic cylinder unit, all three elements being arranged in series. The manual hydraulic pump, is actuated through a pivoted hand lever, and sucks a working liquid from the reservoir and supplies it under pressure into the hydraulic cylinder unit. The hydraulic cylinder unit contains and moves a punch rod; while being moved, the punch rod compress a helical coil spring located within the cylinder. The rod is attached to a piercing punch which moves with respect to a fixed die and thus forms a hole in a sheet-like object clamped between the piercing punch and the fixed die. The punching tool is characterized by the fact that the manual hydraulic pump and the hydraulic cylinder unit are interconnected by an L-shaped tubular connector which has a through hydraulic channel. One end of the tubular connector is rotatingly connected to the manual hydraulic pump so that it can freely rotate around the longitudinal axis of the pump without interruption of communication between the hydraulic channel of the tubular connector and hydraulic channel of the manual hydraulic pump, while the other end of the tubular connector is rotatingly connected to the hydraulic cylinder unit so that it can be freely rotated around an axis which is perpendicular to the first-mentioned axis of said pump. The hydraulic cylinder unit and the tubular connector are mutually interconnected via hydraulic channels which are formed by an annular groove in the periphery of the axial element. The annular groove is connected to the channel inside this element, and the inner surface of the tubular portion is telescopically fitted onto the above-mentioned axial element for free rotation on the latter.
In use, the punching tool of the above-described type is held by hand at the hollow handle, and a fixed die with a hole of a required diameter is put onto a punching rod, if necessary, via a spacing collar. The protruding end of the punching rod is passed through a preformed hole of the sheet to be treated. The piercing punch is threaded onto the punching rod from the side opposite to the fixed die. The hand lever is then placed into a position convenient for operation by turning the manual hydraulic pump unit on the tubular connector with respect to the hydraulic cylinder, the axis of which is perpendicular to the surface of the treated sheet. Alternating the grip and release of the hand lever with respect to the hollow handle causes the supply of oil under pressure from the manual hydraulic pump via the tubular connector to the hydraulic cylinder unit. This in turn causes movement of the ram which slides within the cylinder and compresses the coil spring in contact with the ram. Since the ram pulls the punch rod into the cylinder unit, the piercing punch fits into the fixed die and shears the sheet being worked on. As a result, the preformed hole in this sheet is enlarged to the required diameter. The tool described above can be installed into any required position by rotating the tubular connector with respect to the cylindrical unit about an axis parallel to the axis of the cylinder and the hollow handle, or perpendicular thereto. At the same time, an arbitrary angular position of the manual hydraulic pump with respect to tubular connector can be chosen by rotating the pump on the tubular connector. Thus, at any time the hand lever can be installed in an easy-to-reach position by turning it with respect to the punching rod which is perpendicular to the sheet being treated.